A tau-Restricted Key Agreement Scheme

A one-restricted key agreement scheme is a method by which initially a trusted authority distributes private individual pieces of information to a set of users. Later, each member of any group of users of a given size, referred to as a conference, can compute a common key by exchanging messages over a broadcast channel all users have access to. Such schemes can be used to establish only one common key. In this paper we analyse τ-restricted key agreement schemes. Such schemes allow the computation of up to τ common keys for τ distinct conferences. For certain values of the parameters the scheme that we propose distributes less information than the trivial one obtained by considering τ copies of a one-restricted scheme.